Production of a functionalized polytriazole polymer

ABSTRACT

A method for the production of a functionalized polytriazole polymer, particularly a poly(1,2,4-triazole)-polymer, includes the steps of (a) mixing a hydrazine salt, particularly hydrazine sulfate, with at least an aromatic and/or heteroaromatic dicarboxylic acid and/or at least a dicarboxylic acid derivate in polyphosphoric acid and if necessary further components for obtaining a solution; (b) heating the solution in a protective gas atmosphere for obtaining polyhydrazides and adding aromatic and/or heteroaromatic primary amines to the solution; and (c) precipitating a polymer. If necessary, neutralization in a basic solution may be carried out.

This application is a Divisional application of U.S. patent applicationSer. No. 12/022,237 filed Jan. 30, 2008, which claims priority to GermanPatent Application No. DE 10 2007 005 666.6 filed Jan. 31, 2007, thedisclosures of which are herein incorporated by reference in theirentireties.

TECHNICAL FIELD

The present invention relates to a method for the production of afunctionalized polytriazole polymer and, more particularly, to a methodfor the production of a poly(1,2,4-triazole)-polymer.

Further, the present invention relates to a membrane comprising thepolymer and the use thereof in a fuel cell. The present invention alsorelates to a fiber comprising the respective polymer.

BACKGROUND

Polytriazoles find use in many and varied applications. Popularapplications include the production of membranes for use in fuel cells.Polytriazoles also find applicability in the area of biocompatibleimplants.

Furthermore, they can be used as coating materials in a variety ofdifferent applications.

Poly(1,2,4-triazoles) are heterocyclic polymers and have beensynthesized since the 1940s. Numerous synthesis procedures for polymersare known. Many of these synthesis procedures are for polymers thatinclude 4-phenyl or 4-hydro-1,2,4-triazole-units, such polymers alsobeing characterized by low molecular weights. Aromaticpoly(4-aryl-1,2,4-triazoles) with high molecular weights, on the otherhand, are primarily synthesized in two ways: According to a firstmethod, ditetrazoles and diazidechlorides are used, leading to polymerswith comparably low molecular weights. According to a second method,polymers with high molecular weights are obtained from acyclocondensation of aniline with high molecular weight aromatichydrazides in polyphosphoric acid (PPA).

A method according to the latter process mentioned above is described byHolsen J R, Lilyquist M R in J. Polym. Sci.: Part A Vol. 3 (1965)3905-3917. This method describes a two-step process for the productionof aromatic poly(phenylene)4-phenyle-1,2,4-triazole. Preparation of aprepolymer, an aromatic polyhydrazide, is provided by a polycondensationreaction of terephthaloyl-chloride and isophthaloyl-dihydrazide. Thepolytriazole first produced is cyclocondensed at temperatures between175° C. and 260° C. with aniline in PPA. The reaction times vary between24 hours and 140 hours. At low temperatures, a molecular weight ofbetween 20,000 and 29,000 is realized. The highest inherent viscositiesare obtained when the reaction is carried out at 175° C. for 140 hours.A shorter reaction time with higher temperatures results in polymerswith lower viscosity.

Virpsha, Travnikova, Krongauz, Korshak describe the synthesis ofpolytriazoles in a one-step process, cf. Vysokomol. Soyed., 1969, A11/1,69-72. This process starts with the direct production ofpoly-1,3,4-oxadiazoles by a reaction of a dicarboxylic acid withhydrazine sulfate. The polyoxodiazole obtained intermediately is notisolated from the reaction mixture, and aniline and PPA are added to themixture. The mixture is heated with constant stirring. The production ofpolyoxodiazole occurs at temperatures between 140° C. and 180° C. in areaction time frame between 0.5 hours and 5 hours. The polytriazoles areproduced at temperatures between 215° C. and 220° C. and in a reactiontime frame between 12 hours and 35 hours. The resulting polymer isinsoluble in organic solvents and has a reduced viscosity between 0.42dL/g (deciliter per gram) to 5.1 dL/g measured in sulfuric acid, whereinthe values get smaller as reaction times increase. Furthermore, it isreported that residual hydrazide groups are observed.

In view of the foregoing, there is an interest in producingpolytriazoles that are soluble in organic solvents and contain noresidual hydrazide groups. Furthermore, with regard to the production ofpolytriazoles, lower reaction times, lower reaction temperatures, andresulting high molecular weights are desirable.

To date, polytriazoles have typically been produced in a one-potprocess. These polytriazoles contain residual hydrazide groups and areinsoluble in organic solvents. The residual hydrazide groups are adisadvantage, as they are neither thermically stable nor chemicallystable. Furthermore, long reaction times, e.g., at least twelve hours,and high temperatures are necessary to produce the polytriazoles.

Polytriazoles that are soluble in organic solvents were produced intwo-step synthesis procedures that require more time and hightemperatures. Two polymers are synthesized in these procedures, and theresulting molecular weights are lower. Furthermore, technicaldifficulties arise during commercial production of polytriazoles in atwo-step process.

DE 691 31 529 T2 describes a light-sensitive resin composition that issuitable for the formation of a heat resistant resin sample for use insemiconductors. The resin composition may comprise, for example,polytriazoles and is soluble in organic solvents such asN-methyl-2-pyrrolidone.

U.S. Pat. No. 4,933,083 describes a composite membrane for theseparation of liquids, for example, for use in fuel cells. The compositemembrane comprises polytriazoles (among other materials) and is obtainedfrom a polymer solution with N-methyl-2-pyrrolidone.

U.S. Pat. No. 6,096,898 discloses the production of 1,2,4-triazolene ina one-pot method.

Based on the foregoing, it is an object of the present invention toproduce functionalized polytriazoles in a method of short duration andwith low temperatures, such polytriazoles being easily soluble inorganic solvents and having high molecular weights.

SUMMARY

A method for the production of a functionalized polytriazole polymer,particularly a poly(1,2,4-triazole)-polymer, includes the steps of (a)mixing a hydrazine salt, particularly hydrazine sulfate, with at leastan aromatic and/or heteroaromatic dicarboxylic acid and/or at least adicarboxylic acid derivate in polyphosphoric acid and if necessaryfurther components for obtaining a solution; (b) heating the solution ina protective gas atmosphere for obtaining polyhydrazides and addingaromatic and/or heteroaromatic primary amines to the solution; and (c)precipitating a polymer. If necessary, neutralization in a basicsolution may be carried out.

BRIEF DESCRIPTION OF THE FIGURE

The FIGURE illustrates a chemical reaction of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, a method for the production of afunctionalized polytriazole polymer, particularly apoly(1,2,4-triazole)-polymer, includes the following steps:

-   -   a) mixing a hydrazine salt such as hydrazine sulfate with at        least one aromatic and heteroaromatic dicarboxylic acid and/or        at least a dicarboxylic acid derivative in polyphosphoric acid        and if applicable further components for obtaining a solution,    -   b) heating the solution in a protective gas atmosphere for        obtaining polyhydrazides and adding aromatic and/or        heteroaromatic primary amines, that is amines with a primary        amino group, to the solution, and    -   c) precipitating a polymer.        If applicable, a neutralization step is carried out in a basic        solution to eliminate an etching effect.

The mixing ratio of the aromatic dicarboxylic acids to theheteroaromatic dicarboxylic acids is preferably between 1:99 and 99:1,especially preferred between 1:50 and 50:1. These ratios are independentof the sulfonic acid content of the dicarboxylic acid.

The mixture prepared in step a) comprises especially 1 to 30 wt. %,preferably 2 to 15 wt. %, monomers for the preparation of polytriazoles.

In a preferred embodiment in step b), a first heating of the solution iscarried out in a protective gas atmosphere for obtaining polyhydrazides.Aromatic and/or heteroaromatic primary amines are then added to thesolution. The solution is further heated in the protective gasatmosphere to obtain polyhydrazides.

Another embodiment discloses at least a dicarboxylic acid and/or atleast a dicarboxylic acid derivate comprising a structure of the formula

wherein Ar describes an aromatic or heteroaromatic group, particularlywith substituents and/or a multi ring system, optionally with —O—, —CO—,—C(CH₃)—, —C(CF₃)—, and/or —SO₂— as compounds between the aromaticrings,

-   X describes a group of the formula OR², wherein R² is a hydrogen    atom or a group with 1 to up to 20 carbon atoms,-   Y describes a bond or a group with 1 to up to 20 carbon atoms,-   Z describes a group of the common formula —SO₃R¹ or —PO(OR¹)₂,    wherein R¹ is a hydrogen atom or an alkali metal, and-   q is a whole number between 0 and 4.-   The parameter q preferably takes up the value 1.

The structures are particularly easily obtained by sulfonation of knownand commonly obtained aromatic and heteroaromatic substances.

Preferably the mixture comprises at least an aromatic dicarboxylic acidand a hydrazine salt. The obtained polyhydrazide may have the followingformula:

wherein n is a natural number ≦10, preferably ≦100.

In another preferred embodiment, the solution in step a) comprises atleast an aromatic dicarboxylic acid of the group4,4′-diphenyletherdicarboxylic acid, isophthalic acid, terephthalicacid, phthalic acid, 3-fluorophthalic acid, 5-fluoroisophthalic acid, 2-fluoroterephthalic acid,1,4-naphthalene dicarboxylic acid,1,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid,2,7 naphthalene dicarboxylic acid, diphenic acid, ether,benzophenone-4,4′-dicarboxylic acid, bis(4-dicarboxylphenyl)sulfone,biphenyl-4,4′-dicarboxylic acid, 4-trifluoromethylphthalic acid,2,2-bis(4-carboxyphenyl)hexafluoropropane or the C1-C20-alkylester orC5-C12-arylester thereof.

In another embodiment, the solution in step a) comprises at least aheteroaromatic dicarboxylic acid having in the aromatic ring at least anatom from the group of nitrogen, oxygen, sulfur, and phosphorus.

Preferably at least one dicarboxylic acid from the group ofpyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid,pyridine-2,6-dicarboxylic acid, pyridine-2,4-dicarboxylic acid,4-phenyl-2,5-pyridine dicarboxylic acid, 3,5-pyrazole dicarboxylic acid,2,6-pyrimidine carboxylic acid, 2,5-pyrazine dicarboxylic acid,benzimidazole-5,6-dicarboxylic acid or the C1-C20-alkylesters orC5-C12-arylesters thereof are used.

The heating in step b) is done at temperatures reaching 250° C.,preferably 200° C. Particularly the heating in step b) is done attemperatures in the range of 100° C. and 190° C., particularly preferredbetween 150° C. and 190° C.

Preferably an inert gas is used for the protective gas atmosphere (forexample, a noble gas such as argon or neon and/or nitrogen). Also amixture of different such gases is possible.

The prepolymer in step b) is preferably obtained within a time frame ofone to three hours.

Particularly advantageous is a method, wherein the aromatic and/orheteroaromatic primary amines, in particular containing a sulfonic acidgroup, have a structure of the following formula:

H₂N—Ar—YqZ,

wherein Ar is an aromatic or heteroaromatic group, particularly withsubstituents and/or a multi ring system, optionally with —O—, —CO—,—C(CH₃)—, —C(CF₃),- and/or —SO₂— as bonds between the aromatic rings,

-   wherein Y is a bond or a group with 1 to up to 20 carbon atoms,-   Z is a group of the common formula —SO₃R¹, wherein R¹ is a hydrogen    atom or an alkali metal, and-   q is a whole number between 0 and 4.

Preferably the molar ratio of the aromatic and/or heteroaromatic primaryamines to the polyhydrazides obtained in step b) is essentially at 1:1.It is also advantageous when the molar ratio of the aromatic and/orheteroaromatic primary amines is essentially at 0.4 mol/150 g (moles pergram) to the amount of polyphosphoric acid.

It is particularly desirable to obtain compositions of high molecularweights.

It is also advantageous when a primary amine from the group of aniline,4-aminobenzensulfonic acid, 3 aminobenzensulfonic acid, 4-aminopyridine,4-fluoroaniline, 3-fluoroaniline, 4-quinolinamine and 4-bromoaniline isused.

Another embodiment of the method of the present invention provides forthe first heating to take place in a temperature range between 150° C.and 170° C. and/or the further heating taking place in a temperaturerange between 170° C. and 190° C.

Preferably the polymer in step c) is obtained within a time frame of twoto five hours.

The object of the invention is furthermore attained by a functionalizedpolytriazole polymer obtained by an inventive method.

The molecular ratio of nitrogen to carbon (N/C) lies in thefunctionalized polytriazole polymer advantageously between 0.168 and0.175, preferably between 0.172 and 0.175.

N/C, the molar ratio of nitrogen to carbon, is mathematicallydetermined. The conversion of oxadiazole groups into triazole rings canbe determined from the N/C according to the following equation:

conversion(%)=[(N/C−0.167)/0.008]×100.

If the value for N/C is 0.167, it means that 100% of the oxadiazolereacted with a diphenylether group. Unconverted oxadiazole groups arenot disadvantageous, as these groups are as stable as the triazolerings. But residual hydrazide groups are not desired, as such groups areneither thermically nor chemically as stable as oxazole groups.

Preferably, the molar ratio S/C of sulfur to carbon is between 0.018 and0.400, particularly between 0.133 and 0.400, and particularly preferredbetween 0.235 and 0.400.

S/C, the molar ratio of sulfur to carbon is determined mathematically.

A particular embodiment of the invention provides for aromatic and/orheteroaromatic primary amines with at least a sulfonic acid group beingused. Thus, the influence of the reaction time and reaction temperatureon the ratio N/C, that is, the conversion of prepolymer intopolytriazole, can be determined. Moreover, the effect of bothparameters, namely, reaction time and reaction temperature on S/C, thatis, the sulfonizing degree of the polytriazoles can be determined.

The molecular weight of the inventive polymer is preferably in the rangeof 10⁵ g/mol (grams per mole) or above.

The intrinsic viscosity of the polymer, measured in dimethylsulfoxide,is preferably between 1 and 5 dL/g, particularly preferred between 3 and4 dL/g.

The polymer distinguishes itself by being easily soluble in aproticpolar solvents and in strong acids such as for example, sulfuric-,hydrochloric-, and phorphoric acid.

The high viscosity is brought upon especially by the high molecularweight. The polymer comprises preferably recurring triazole units with ahomopolymer of the formula (I) or a copolymer of the formula (II),comprising at least two units being different from each other. Thepolymers can be present in the form of block copolymers (diblock ortriblock), in the form of statistical copolymers, periodic copolymers,and/or alternating copolymers, wherein m is also a natural number.

The objective is solved also by a membrane and a fiber containing theinventive polymer.

The membrane can be used advantageously in a fuel cell.

In the following, the invention is disclosed without restriction of thegeneral inventive thought with two embodiments and with a drawing.Concerning the disclosure of inventive details not fully explained inthe text, the embodiments and drawing are referred to.

Example 1 Polymer Synthesis

4,4′-diphenylether-dicarboxylic acid (DPE) and hydrazinesulfate (HS)react for one hour at 160° C., then the reaction temperature isincreased to 180° C.

4-aminobenzenesulfonic acid is added to the reaction vessel thereafter,wherein a further two hour reaction time is provided. The molarsolubility rate (PPA/HS) and the molar monomer rate (HS/DPE) are keptconstant at 10 and 1.2, respectively. A molar ratio of polyhydrazide,formed in situ, to 4-aminobenzenesulfonic acid of 1:1 is used. Aftercompletion of the process, the reactive medium is put into lukewarmwater containing 5 wt. %/vol. sodium hydroxide solution to precipitatethe polymer. The pH-value of the polymer suspension is controlled (see,for example, Gomes et al., Polymer 45 (2004) 4997-5004). In this way, adark blue fiber is obtained, which is first cleaned in distilled waterand then dried in a vacuum furnace for 48 hours at 100° C.

The ratio N/C of the synthesized polymer is 0.174 and the ratio S/C is0.058. The average molecular weight is 560,000. The average molecularweight of the polymer samples are determined with an apparatus of thetype Viscotek SEC. The device supply is calibrated withstandard-polystyrol by Merck, comprising an average molecular weight inthe range between 309 and 944,000 g/mol. A solution with 0.05 M lithiumbromide in DMAC is used as a carrier. The conversion of oxadiazolegroups into triazole rings is at 88%, calculated according to theabove-mentioned equation. Thus a polymer is obtained, being soluble inorganic solvents such as NMP, DMSO, DMF and does not comprise residualhydrazide groups according to the TGA-FTIR-analysis.

Production of the Polymer Membrane

1 g polymer is dissolved in 14 g N-methyl-2-pyrrolidone (about 7 wt. %).The solution is stirred for 4 hours and poured on a glass plate, earlierrendered hydrophobic with octadecyl-trichlorosilane and heated to 65° C.to evaporate the solvent. After pouring, the sulfonisedpoly(4-aryl-1,2,4-triazole)-membrane is dried at 80° C. for 24 hours inthe vacuum furnace. The thickness of the dark blue membrane iseventually 90 μm.

Example 2 Polymer Synthesis

4,4′-diphenylether-dicarboxylic acid (DPR) and hydrazinesulfate (HS)react for three hours at 160° C., then the reaction temperature isincreased to 180° C. Thereafter, 4-aminobenzenesulfonic acid is added toa reaction vessel for another two hours of reaction time. The molarsolubility rate (PPA/HS) and the molar monomer rate (HS/DPE) are keptconstant at 10 and 1.2, respectively. A molar ratio of polyhydrazide,formed in situ, to 4-aminobenzensulfonic acid of 1:1 is used. Aftercompletion of the process, the reactive medium is put into lukewarmwater containing 5% wt./vol. sodium hydroxide solution to precipitatethe polymer. The pH-value of the polymer suspension is controlled (see,for example, Gomes et al., Polymer 45 (2004) 4997-5004.) In this way, afiber is obtained, which is first cleaned in distilled water and thendried in a vacuum furnace for 48 hours at 100° C. The ratio N/C of thesynthesized polymer is 0.173 and the ratio S/C is 0.094. The averagemolecular weight is 230,000. The average molecular weight of the polymersamples are determined with an apparatus of the type Viscotek SEC. Theconversion of oxadiazole groups into triazole rings is at 75%,calculated according to the above-mentioned equation. Thus a polymer isobtained, being soluble in organic solvents such as NMP, DMSO, DMF anddoes not comprise residual hydrazide groups according to theTGA-FTIR-analysis.

Production of Polymer Membrane

1 g polymer is dissolved in 14 g N-methyl-2-pyrrolidone (about 7 wt. %).The solution is stirred for 4 hours and poured on a glass plate, earlierrendered hydrophobic with octadecyl-trichlorosilane and heated to 65° C.to evaporate the solvent. After pouring, thepoly(4-aryl-1,2,4-triazole)-membrane containing sulfonic acid is driedat 80° C. for 24 hours in the vacuum furnace. The thickness of the darkgreen membrane is eventually 85 μm.

A further embodiment of the invention is depicted in the FIGURE.

The FIGURE shows two alternative mechanisms A and B for the productionof a functionalized polytriazole-polymer using aromatic and/orheteroaromatic primary amines with at least one sulfonic acid group. TheFIGURE shows the influence of the reaction times t₁ and t_(T) on N/C,characteristic for the conversion degree of prepolymer intopolytriazole, and with regard to S/C (the sulfonizing degree of thepolytriazole). The first reaction time t₁ and the total reaction timet_(T) are decisive factors for the values N/C and S/C. On average, thepreferred reaction time t₁ is in the range between one and three hours,particularly between one and two hours. The total reaction time t_(T) ispreferably between 2 hours and 16 hours, more preferably between 2 hoursand 11 hours, and even more preferably between 2 hours and 5 hours.

A high value for t₁ will be advantageous for a polymerization accordingto mechanism A, that is, the synthesis of poly(1,2,4-triazole) with highvalues for N/C and S/C. A low value for t₁ will in turn benefit areaction according to mechanism B, so that both mechanisms A and B takeeffect at the same time and a lower value for S/C is obtained.

1. A functionalized polytriazole polymer obtained by a method comprisingthe steps of: a) mixing a hydrazine salt with at least one of adicarboxylic acid and a dicarboxylic acid derivative in polyphosphoricacid to obtain a solution; b) heating the solution in a protective gasatmosphere and adding at least one primary amine to the solution to formpolyhydrazides, wherein said primary amine is selected from a groupconsisting of aromatic primary amines and heteroaromatic primary amines;and c) precipitating a polymer from the solution.
 2. The functionalizedpolymer according to claim 1, wherein a molar ratio N/C of nitrogen tocarbon is between 0.168 and 0.175.
 3. The functionalized polymeraccording to claim 1, wherein a molar ratio S/C of sulfur to carbon isbetween 0.018 and 0.400.
 4. The functionalized polymer according toclaim 1, having a molecular weight approximately in a range of 10⁵ g/molor above.
 5. The functionalized polymer according to claim 1, having anintrinsic viscosity, measured in dimethylsulfoxide, within a rangebetween 1 and 5 dL/g.
 6. The functionalized polymer according to claim1, wherein the functionalized polymer is soluble in aprotic polarsolvents and in strong acids.
 7. A membrane comprising a functionalizedpolymer according to claim
 1. 8. The membrane according to claim 7 foruse in a fuel cell.
 9. A fiber comprising a functionalized polymeraccording to claim 1.